Catheter Air Management System

ABSTRACT

An air management system is described for removing and reintroducing a desired amount of air into an air passage of a pressure measurement catheter. More specifically, the system includes a cylindrical housing, check valves in communication with the housing and an moveable shaft with multiple sealing members along its length. As the shaft is moved within the housing, a piston member causes the residual air in the catheter air passage to be evacuated to a defined negative pressure. Further movement of the shaft causes a piston member to inject a predetermined volume of air into the catheter air passage. In this respect, periodic adjustments of the piston member returns the volume of air in a variable volume chamber to one that is unaffected by residual volume in the chamber and that provides an optimum volume of air to maximize the time the sensor can function accurately between recharging events.

RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 13/752,079 filed Jan. 28, 2013 entitled CatheterAir Management System, which is a continuation of U.S. patentapplication Ser. No. 12/606,169 filed Oct. 26, 2009 entitled CatheterAir Management System (now U.S. Pat. No. 8,360,988 issued Jan. 29,2013), which claims priority to U.S. Provisional Application Ser. No.61/197,042 filed Oct. 24, 2008 entitled Catheter Air Management System,and to U.S. Provisional Application Ser. No. 61/209,839 filed Mar. 12,2009 entitled Catheter Air Management System, all of which are herebyincorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

Presently, biologically compatible air-based pressure monitoringcatheters are used in a number of medical applications to monitorpressure at various locations within a mammalian body. For example,air-based pressure monitoring catheters may be inserted into the skullof a patient thereby permitting the external monitoring of intra-cranialpressure.

Currently, a number of air-based pressure monitoring catheters have beendeveloped. Generally, these air-based pressure monitoring catheterscomprise a catheter having an air lumen formed therein whichcommunicates with a bladder positioned at or near its distal end. Inaddition, the catheter includes a connector located at or near itsproximal end which may be connected to an external pressure transducer.During use, the volume of the bladder attached to the catheter changesas pressure varies in accordance with Boyle's Law (P₁V₁=P₂V₂). As aresult, the pressure of the gas within the catheter becomes equal tothat of the environment surrounding the bladder. The media surroundingthe bladder must be capable of movement to accommodate the variations inbladder volume as pressure changes.

The use of air-based pressure monitoring catheters in low or negativelypressurized environments has proven problematic. When the proximalconnector is open to atmospheric pressure in the process of periodicallyreplacing air lost by diffusion through the bladder, the externalpressure extant in the body site monitored on a bladder will expelresidual air from the bladder. If the pressure is low or negative, asignificant amount of residual air may remain in the bladder. The amountof air injected is intended to be sufficient to keep the bladder in anactive state for a period of 8 hours. If this volume is added to theresidual air in a bladder that has not been completely collapsed by theenvironment around it, the sum of the residual air and injected airexceed the intrinsic volume of a fully shaped bladder. Should thishappen, a positive pressure is established in the bladder. The bladderis now unable to read pressure below the internal pressure created.

Air management systems such as those seen in U.S. Pub. No. 2007/0208270and U.S. Pat. No. 6,447,462, which are both herein incorporated byreference, allow a user to adjust the amount of air in a system. Forexample, these systems allow a user to vent the air passage of thecatheter to the open environment, then charge the passage with an amountof air. While these systems function adequately when residual air in thebladder is adequately expressed by pressure from the monitored bodysite, they over pressurize the bladder if the monitored site pressurehas not sufficiently collapsed the bladder prior to the injection ofair. An optional design that avoids over pressurizing the bladder byreducing the amount of air injected is not attractive as the lessoramount of air injected reduces the effective operating time between airrecharging events in a case where the bladder has been largely collapsedby pressure in the body site measured. The intent of the invention is topreserve the desired operating time between air-charging events in amanner that precludes the possibility of pressurizing the bladder.

SUMMARY OF THE INVENTION

A preferred embodiment according to the present invention includes anair management system for removing and reintroducing a desired amount ofair into an air passage of a pressure measurement catheter. Morespecifically, the system includes three cylinders within which can movea shaft with three sealing members along its length. The system includescheck valves in communication with one of the cylinders. As the shaft ismoved within the set of cylinders, it causes the residual air in thecatheter air passage to be evacuated to a negative pressure defined byone check valve. Further movement of the piston member injects apredetermined volume of air into the catheter air passage. This air isfrom excess air present in the evacuation cylinder and held by a checkvalve at a predetermined pressure (e.g., 0.5 PSI), not from exposure tothe open atmosphere. Evacuating the catheter to a fixed negativepressure prior to injecting air eliminates the possibility thatvariations in the residual volume in the bladder can affect the pressurereading or the operating time.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of which embodiments ofthe invention are capable of will be apparent and elucidated from thefollowing description of embodiments of the present invention, referencebeing made to the accompanying drawings, in which

FIG. 1 illustrates a perspective view of a catheter air managementsystem according to a preferred embodiment of the present invention;

FIG. 2 illustrates a perspective view of the internal components of abody housing of the system of FIG. 1;

FIG. 3 illustrates a perspective view of piston members and pistoncylinders from FIG. 2;

FIG. 4 illustrates a side view of the piston members and pistoncylinders from FIG. 3;

FIG. 5 illustrates a cross sectional view of the piston members andpiston cylinders from FIG. 4 taken along lines A-A;

FIGS. 6-8 illustrate simplified cross sectional views of the pistonmembers in various positions within the piston cylinders; and,

FIG. 9 is an example pressure graph of an air management systemaccording to a preferred embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Specific embodiments of the invention will now be described withreference to the accompanying drawings. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art. Theterminology used in the detailed description of the embodimentsillustrated in the accompanying drawings is not intended to be limitingof the invention. In the drawings, like numbers refer to like elements.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIG. 1 illustrates an air catheter management system 100 according to apreferred embodiment of the present invention. The system 100 allows auser to charge an air passage in communication with a catheter having apressure sensing lumen (e.g., such as that shown in U.S. ProvisionalApplications 61/197,039 and 61/197,041, the contents of which are herebyincorporated by reference). The air passage of the catheter is connectedto the catheter connection port 104.

The system 100 also includes a monitor cable 108 that communicatesbetween a pressure monitor (not shown) and a transducer 115 (FIG. 2)within the housing 102. The monitor cable preferably includes multiplewires that provide an excitation voltage for the transducer and voltagemeasurements to the monitor. A monitor connector 110 (e.g., a Marquetteconnector) connects to a desired monitor type to display a pressurereading to a user.

Proper operation of an air-based pressure sensor requires that apredetermined amount of air reside in the bladder. Over time, air candiffuse out of the catheter, the pressure lumen of the catheter, orother portions of the arrangement. The system 100 allows the user toperiodically replace air lost by diffusion by pulling out a handle 106,then pushing that handle back into to the housing 102 of the system 100.This action removes the air in the system 100 to a predetermined vacuumpressure, and then adds a predetermined amount of air back into thesystem.

Preferably, the housing further includes a set of indicators 105, suchas lights, that indicate when the expected operating life of the sensorbetween recharging events has been reached and a recharging event isrequired. Preferably, the housing 102 (or optionally the transducer) mayinclude a timer that counts a predetermined period of time (e.g., 8hours) before signaling that it is time to recharge (i.e., pull out thehandle 106 and push in the handle 106).

Further, the housing 102 may include a microprocessor or otherelectronics that connects to the transducer 115 to obtain a pressurereading, then convert this reading to a form recognizable to thepressure monitor (e.g., mV/mmHg/V). This further allows the indicators105 on the housing 102 to signal a need for a recharge of the system 100at different times. For example, if a catheter is not connected to theport 104, the pressure will be zero (i.e., 1 ATM) and therefore theindicator will turn red, signaling to the user that the catheter iscurrently connected. In another example, if the catheter is connected tothe port 104 and inserted into the patient, a positive pressure mayregister and cause the indicator to signal a recharge to place thedesired amount of air into the system. Alternately the form of thepressure wave can be monitored to determine if the catheter is connectedto the port 104.

FIG. 2 illustrates an internal view of the housing 102 and some of itscomponents. The monitor cable 108 enters the housing 102 and connects toelectronics, such as a microprocessor, that are in communication withthe transducer 115. Hence, the electronics can communicate with both thetransducer 115 and the pressure monitor. The transducer 115 preferablyincludes a manifold 107 over its top which provides a connectioninterface for a tube (not shown) with the port 104. This passage throughthe port 104 and the transducer 115 within the housing 102 is furtherconnected to a charging assembly 112 via connecting passage 118 (FIG.3). Hence, as the handle 106 is moved out and in, the air passage of thesystem 100 is charged with a predetermined amount of air.

FIGS. 3 and 4 illustrate various views of the charging assembly 112.Preferably, the charging assembly 112 is composed of an outer pistonhousing or piston cylinder 113 through which a piston member 120 movesinto and partially out of. Preferably, this piston cylinder 113 isgenerally cylindrical in shape. The piston member 120 is connected tothe handle 106 at end 122.

As described in more detail below, the charging assembly 112 achieves adesired air pressure through passage 118 by the movement of the pistonmember 120 and two check valves 114 and 116 that are set to open atdifferent pressures. Preferably, these check valves also include airfilters 115 to prevent any particles, dirt or other contamination intothe system (FIG. 4).

Turning to FIG. 5, a cross sectional view of the charging assembly 112is shown. The piston member 120 preferably includes a first section 121adjustably connected to a second section 130 (e.g., via a thread) toallow the length of the piston member 120 to be adjusted. As will becomeclear with the explanation below, this adjustment can modify an amountof air moved by the piston member 120. Also, this threading allows thepiston member 120 to be easily assembled within the housing 113.

The piston member 120 also includes at least three sealing members(e.g., o-rings): a first sealing member 124, a second sealing member 126and a third sealing member 128. These sealing members 124, 126 and 128contact an inner surface of the housing 113 so as to prevent passage ofair and create two sealed air spaces between each other. Preferably,these sealing members are located in recessed areas of the piston member120 and are composed of fluroelastomer (Viton).

Preferably, the passage within the housing 113 has three different areasof different diameter: area 132, area 134 and area 136. Preferably area134 is located between the other two areas 132 and 136 and has a smallerdiameter than these two areas 132 and 136. Since the piston member 120also has areas of different diameters, the piston member 120 isrestricted from moving (i.e., restricted from being pushed in or pulledout beyond a predetermined position).

The section 134 also includes an opening in communication with passage118, through which air is pulled from or pushed into the air passage ofthe system 100. Further, this area is coupled to the first check valve114 configured to allow outside air to enter the system at apredetermined air pressure and the second check valve 116 configured toallow air in the housing 113 to be released into the outside environmentat a predetermined air pressure. In other words, the first check valve114 opens at a predetermined negative pressure and the second checkvalve 116 opens at a predetermined positive pressure. For example, thevalve 114 may open when a pressure in the housing 113 reaches −0.5 PSIand the valve 116 may open when a pressure in the housing 113 reaches+0.5 PSI.

FIGS. 6-8 illustrate a simplified drawing of the charging assembly 112in various positions. Beginning with FIG. 6, the piston member 120 isillustrated in a “pushed in” position (i.e., the handle 106 is locatednear the housing 102). In this position, the passage 118 is isolated bysealing members 124 and 126, preventing air from entering or leaving thepassage of the system 100.

As seen in FIG. 7, as the user begins to pull out the piston member 120,air within the larger-volume area 136 is forced into the smaller volumearea of area 134, thereby increasing the air pressure. Once the airpressure between the sealing members 126 and 128 reaches a predeterminedpositive pressure, the check valve 116 releases any excess air tomaintain a pressure at the predetermined positive pressure. As thepiston member 120 continues to be pulled out, the sealing member 126passes the passage 118 and therefore opens the area between sealingmembers 126 and 128 to the air passage of the system 100 (i.e., thepassage 118, the air passage of the catheter and the transducer 115).Since the air pressure has been limited by the check valve 116, thepressure lumen or bladder on the pressure measuring catheter is notdamaged. Hence, the predetermined opening pressure of this check valve116 (and as discussed below valve 114) should be selected, in part,based on the pressure rating of the pressure catheter.

In FIG. 8, the piston member 120 is pulled out from the chargingassembly 112 as far as possible. In this position, the area between thesealing member 124 and sealing member 126 becomes open to the airpassage of the system 100 (i.e., the passage 118, the air passage of thecatheter and the tranducer 115). In this respect, the area betweensealing member 124 and 128 is at about the positive predeterminedpositive pressure that check valve 116 opens (e.g., +0.5 PSI).

Once the piston member 120 has been pulled out as far as it will go, itcan be pushed back in. Returning once again to FIG. 7, as the pistonmember 120 is pushed in, the sealing member 126 once again engages area134. The air between sealing member 126 and 128 moves from smallerdiameter region 134 to larger diameter region 136 and therefore reducesthe pressure in the system 100. As the pressure reaches a negativepredetermined amount (e.g., −0.5 PSI), the check valve 116 opens to letin additional air to maintain that predetermined pressure. Hence, thepassages of the system 100 remain at the predetermined air pressure.

As the piston member 120 continues to be pushed inwards, pressure buildsbetween sealing member 124 and 126 as the air moves from the largerdiameter region 132 to the smaller diameter region 134. As seen in FIG.6, the sealing member 126 passes passage 118, allowing the high pressureair between sealing members 124 and 126 to pass into the system 100. Inthis respect, the system 100 progresses from a predetermined negativepressure followed by the injection of a known volume of air, since thevolume of air between the sealing members 124 and 126 is added to thesystem 100. In other words, system 100 has been evacuated to a definednegative pressure, then injected with a predetermined quantity of air.

FIG. 9 illustrates an example pressure wave measurement of an airmanagement system during movement of the piston member 120. For example,area 1 illustrates the pressure after full injection of the known airvolume of the piston member 120. Area 2 illustrates the initialretraction of the piston member where pressure decreases due to volumeincreases in the housing 113 (the system remains isolated from the checkvalve). Area 3 illustrates a continued retraction as the system pressureincreases due to volume decreases in the housing 113 (the check valve116 maintains a position predetermined pressure). Area 4 illustrates theinitial actuation inwards of the piston member 120 where the pressure ismaintained. Area 5 illustrates the continued inward movement of thepiston member 120 where the check valve 114 limits the negativepressure. Finally, area 6 illustrates the final movements of the pistonmember 120 as the known volume of air is injected back into the system(i.e., the catheter).

Depending on the predetermined opening pressure of the check valves 114and 116, the diameter of the areas 132, 134 and 136, and the spacing ofthe sealing members 124, 126 and 128, the final pressure in the systemcan be determined. The injection volume is equal to the area betweensealing member 124 and 126 times the distance from transition of area132 to area 134 and the final location of 126 at the end of the stroke.Preferably, this final pressure is a value that allows the transducerand the bladder/lumen on the distal end of the measurement catheter toachieve accurate results. In this respect, a second shut off valve,which is typically required in use with prior art air managementsystems, is unnecessary.

In one example, the sealing members 124 and 126 are spaced at about0.160 inches from each other and sealing members 126 and 128 are spacedat about 0.800 inches from each other. The diameter of the piston member120 between the sealing members 124 and 126 is about 0.204 inches andthe diameter of the piston member 120 between the sealing members 126and 128 is about 0.173 inches. The diameter of the first area 132 isabout 0.205 inches, the diameter of the second area 134 is about 0.173inches and the diameter of the third area 136 is about 0.238 inches.

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. Accordingly, it is to be understood that the drawingsand descriptions herein are proffered by way of example to facilitatecomprehension of the invention and should not be construed to limit thescope thereof.

What is claimed is:
 1. A catheter air management system, comprising: anair pressure communication passage; a charging assembly connected tosaid air pressure communication passage; a check valve connected to saidair pressure communication passage and further opening at apredetermined pressure; a catheter connection port connected to said airpressure communication passage and selectively connectable to theinternal passage of a catheter having an air bladder; and; a pressuretransducer connected to said air pressure communication passage; whereinsaid charging assembly adjusts a pressure level of air inside said airpressure communication passage and further injects a predeterminedvolume of air; and, wherein said pressure transducer measures saidpressure level of air within said air pressure communication passage. 2.The catheter air management system of claim 1, further comprising amonitor cable that is connectable to a pressure monitor and furtherconveys pressure data from said pressure transducer to said pressuremonitor.
 3. The catheter air management system of claim 2, furthercomprising an electronic assembly in communication with said pressuretransducer and further providing said pressure data to said pressuremonitor.
 4. The catheter air management system of claim 2, furthercomprising a monitor connector located at an end of said monitor cableand being connectable with a said pressure monitor.
 5. The catheter airmanagement system of claim 1, further comprising an indicator lightsignaling a pressure recharging status.
 6. The catheter air managementsystem of claim 1, wherein said check valve further comprises an airfilter that filters air passing through said check valve and into saidair pressure communication passage.
 7. The catheter air managementsystem of claim 1, wherein said charging assembly further comprises apiston member movable to a first position that removes air from said airpressure communication passage, and movable to a second position thatinjects air into said air pressure communication passage.
 8. A catheterair management system, comprising: an air pressure communicationpassage; a charging assembly connected to said air pressurecommunication passage; a check valve connected to said air pressurecommunication passage and further opening at a predetermined pressure; acatheter connection port connected to said air pressure communicationpassage; and; a pressure transducer connected to said air pressurecommunication passage; wherein said charging assembly evacuates said airpressure communication passage to said predetermined pressure andfurther injects a predetermined volume of air.
 9. The catheter airmanagement system of claim 8, wherein said pressure transducer measuresa pressure level of air within said air pressure communication passage.10. The catheter air management system of claim 8, wherein said chargingassembly further comprises a piston member movable to a first positionthat evacuates air from said air pressure communication passage, andmovable to a second position that injects air into said air pressurecommunication passage.
 12. The catheter air management system of claim8, wherein said check valve further comprises an air filter that filtersair passing through said check valve and into said air pressurecommunication passage.
 12. The catheter air management system of claim8, further comprising an indicator light signaling a pressure rechargingstatus.
 13. The catheter air management system of claim 8, furthercomprising a monitor cable that is connectable to a pressure monitor andfurther conveys pressure data from said pressure transducer to saidpressure monitor.
 14. The catheter air management system of claim 13,further comprising an electronic assembly in communication with saidpressure transducer and further providing said pressure data to saidpressure monitor.
 15. A method of using a catheter air managementsystem, comprising: actuating a charging assembly of a catheter airmanagement system to evacuate an air pressure communication passage to apredetermined pressure and into an air lumen and air bladder of acatheter; actuating said charging assembly of said catheter airmanagement system to inject a predetermined volume of air into said airpressure communication passage and into said air lumen and said airbladder of said catheter; measuring a pressure within said air pressurecommunication passage; and, providing a pressure measurement to apressure monitor.
 16. The method of claim 15, wherein said actuatingsaid charging assembly of said catheter air management system toevacuate said air pressure communication passage to said predeterminedpressure further comprises moving a piston to a first position within apiston housing.
 17. The method of claim 16, wherein actuating saidcharging assembly of said catheter air management system to inject saidpredetermined volume of air into said air pressure communication passagefurther comprises moving said piston to a second position within apiston housing.